Field of the Invention
The present invention relates to a conductive member to be used in an electrophotographic image-forming apparatus.
Description of the Related Art
Additional lengthening of the lifetime of an electrophotographic apparatus has been required in recent years. Accordingly, slight changes in its physical properties that have not been perceived as problems so far may cause image defects owing to its long-term use. In particular, a change in its electrical resistance value serves as an important factor for high durability of a conductive member.
A conductive member including a conductive layer obtained by adding an ionic conductive agent to a polar polymer such as a hydrin rubber to adjust its electrical resistance value has been proposed as such a conductive member that unevenness in its electrical resistance value has been alleviated. However, when the ionic conductive agent is used, the ionic conductive agent may be unevenly distributed (localized) in the conductive layer owing to long-term use of the member. Possible causes for the foregoing are as described below. The time period for which a DC voltage is applied to the conductive member at the time of its use is long. In addition, as the conductive layer repeatedly receives a stress, an ion exchange group of the ionic conductive agent undergoes ionic dissociation, and hence an anion and a cation move in the conductive layer to be unevenly distributed. In particular, the uneven distribution of the ion exchange group in the conductive layer increases the electrical resistance value of the conductive member.
In addition, the long-term application of the DC potential to the conductive member and the repeated application of the stress to the conductive layer prompt the bleedout of a low-molecular weight component in the conductive member toward the surface of the conductive layer. The bleedout of the low-molecular weight component toward the surface of the conductive layer leads to the contamination of the surface of a photosensitive member.
To cope with such problems, in Japanese Patent Application Laid-Open No. 2006-189894, a specific quaternary ammonium salt capable of reducing the electrical resistance value even when added in a small amount is used as an ionic conductive agent. In addition, in Japanese Patent Application Laid-Open No. 2001-273815, the bleeding and blooming of an ionic conductive agent are suppressed by using a quaternary ammonium salt having an OH group.